make it easier to configure SSL

[totaam]

provide a GUI via pinentry so that users can more easily accept new self-signed certificates and ignore address mismatch, etc

Some preparatory refactoring done in: 0cc4361 + 874ddc9.
Improved debug logging: 76a7bbd

This feature will require Python 3.7 or later so that we can retrieve the SSLCertVerificationError.verify_code: 5069ebd

[totaam]

This works reasonably well but is being seriously hampered by a bug in pinentry:

cat > notok << EOF
SETPROMPT whatever
SETDESC desc
SETNOTOK please-show-this
CONFIRM
EOF
cat notok | pinentry

This does not show the please-show-this option, which is honoured by pinentry-gtk, pinentry-gtk-2 and pinentry-qt.

So we can't ask the user if he wants to permanently save the host key / skip the hostname check.

[basilgello]

Which distro does the bug manifest?

[totaam]

Which distro does the bug manifest?

@basilgello That will be all of them: Fedora 34, Ubuntu 21.04 and 20.04, Debian Buster and Bullseye.
But as per above, only with the gtk variant, the other variants honour it.

[totaam]

And pinentry just doesn't look very good at all on MacOS and MS Windows so we just re-use the dialogs we already have instead: 30d958a, and lots of other small updates - not all recorded against this ticket in the git commit message.
Works well enough on all platforms.

[totaam]

Follow up in #4288